Heart failure (HF) is one of the most common causes of in-hospital mortality for patients with cardiac diseases. Heart failure is typified by the inability of the heart to pump enough blood to meet the body's metabolic requirements for oxygen and nutrients leading to discrepancies between myocardial oxygen supply and demand. Congestive heart failure annually leads to millions of hospital visits internationally. Congestive heart failure is the description given to a myriad of symptoms that can be the result of the heart's inability to meet the body's demand for blood flow. In certain pathological conditions, the ventricles of the heart become ineffective in pumping the blood, causing a back-up of pressure in the vascular system behind the ventricle.
The reduced effectiveness of the heart is usually due an enlargement of the heart. A myocardial ischemia may, for example, cause a portion of a myocardium of the heart to lose its ability to contract. Prolonged ischaemia can lead to infarction of a portion of the myocardium (heart muscle) wherein the heart muscle dies and becomes scar tissue. Once this tissue dies it no longer functions as a muscle and cannot contribute to the pumping action of the heart. When the heart tissue is no longer pumping effectively, that portion of the myocardium is said to be hypokinetic, meaning that it is less contractile than the uncompromised myocardial tissue. As this situation worsens, the local area of compromised myocardium may in fact bulge out as the heart contracts, further decreasing the heart's ability to move blood forward. When local wall motion moves in this way, it is said to be dyskinetic, or akinetic. The dyskinetic portion of the myocardium may stretch and eventually form an aneurysmic bulge. Certain diseases may cause a global dilated myopathy, i.e., a general enlargement of the heart when this situation continues for an extended period of time.
As the heart begins to fail, distilling pressures increase, which stretches the ventricular chamber prior to contraction and greatly increases the pressure in the heart. In response, the heart tissue reforms to accommodate the chronically increased filling pressures, further increasing the work that the now comprised myocardium must perform.
This vicious cycle of cardiac failure results in the symptoms of congestive heart failure, such as shortness of breath on exertion, edema in the periphery, nocturnal dypsnia (a characteristic shortness of breath that occurs at night after going to bed), waking, and fatigue, to name a few. The enlargements increase stress on the myocardium. The stress increase requires a larger amount of oxygen supply, which can result in exhaustion of the myocardium leading to reduced cardiac output of the heart.
The left ventricle's inability to generate sufficient cardiac output, i.e. HF, is commonly associated with left ventricular systolic (emptying of left ventricular chamber) dysfunction, but its symptoms may also arise as a result of diastolic (filling of left ventricular chamber) dysfunction (with or without the presence of systolic dysfunction). The term “diastolic dysfunction” refers to changes in ventricular diastolic properties that have an adverse effect on ventricular diastolic pressures and ventricular filling.
An integral part of normal diastolic filling is the contribution of the left ventricular (LV) elastic recoil forces to the LV filling. Elastic recoil forces are generated within healthy myocardium during systolic shortening. The magnitudes of elastic recoil forces are inversely proportional to the volume of the LV, i.e., they increase as the LV volume decreases. Their contribution is important in early diastole because they allow rapid and enhanced early filling by assisting the expansion of the left ventricle.
In a case of ventricular enlargement and/or the decrease of myocardial function due to hypertrophy the left ventricular elastic recoil forces may be diminished or nonexistent, therefore ceasing to assist early ventricular filling and leading to an increase of the ventricular filling pressure.
Intervention to alleviate the resultant symptoms of the physical changes described above may offer great benefit to patients with heart disease. Administration of vasodilators, diuretics, sodium channel blockers, and inotropic agents have been used to reduce the number of acute events and slow the advance of disease, but cannot reverse the physical changes to the heart. Surgical intervention can reduce the volume of the ventricle such that cardiac function is improved but carries high risk for the patient. Other less invasive modes of intervention offer improved function while reducing risk for the patient during and after the procedure.
Additional background may be described in each of the following publications, each of which is incorporated by reference:
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